Extracellular matrix macromolecules--proteoglycans, glycosaminoglycans, and collagens--which play important structural roles in adult connective tissue may have significant regulatory functions in the control of cell behavior during embryogenesis as well as during tissue remodelling in the adult. This research project is designed to define further these latter functions. Using a specific developmental model--the developing chick embryo limb--I have begun to characterizethe proteoglycans synthesized by "soft" and skeletal tissues at progressive stages of limb development and then to study the abilities of these macromolecules to interact with collagen. These interactions are presumed to reflect the biochemical interactions which occur in vivo in the formation of extracellular matrices. Initial studies suggest that during limb development a transition may occur from a population of proteoglycans in the 4 day mesenchymal limb bud which are non-reactive with collagen to a population of reactive proteoglycans in the cartilage of 8 day limb bud. In addition, using purified cartilage proteoglycans and collagens, chemically defined substrates have been prepared and tested for their abilities to promote skeletal (cartilage) differentiation. Initial studies suggest that cartilage specific (type II) collagen acts to induce or stabilize the differentiation of limb bud mesenchyme into chondrocytes, under conditions when in vitro chondrogenesis will not otherwise occur.